Integrated circuit die having a split solder pad

ABSTRACT

The invention relates to an electronic system comprising:
         an integrated circuit die having:
           at least 2 bond pads   a redistribution layer, said redistribution layer having:
               at least a solder pad comprising 2 portions arranged to enable an electrical connection between each other by a same solder ball placed on said solder pad, but electrically isolated of each other in the absence of a solder ball on the solder pad   at least 2 redistribution wires, each one connecting one of the 2 portions to one of the 2 bond pads,
 
a second bond pad connected via a second redistribution wire to a second portion of the solder pad being dedicated to testing said integrated circuit die
   
               
           a grounded printed circuit board track, a solder ball being placed between the solder pad and the printed circuit board track.

This application claims priority from European patent application No. 16184545.8 filed on Aug. 17, 2016, the entire disclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a pad for a solder ball, called solder pad, in a redistribution layer of an integrated circuit die.

BACKGROUND OF THE INVENTION

An integrated circuit (IC) die (also called chip) is classically put into a protective package acting as a mechanical interface between said integrated circuit die and a printed circuit board (PCB). A very large number of different types of package exist, which are basically separated into two main techniques.

In the traditional wire-bond packaging technique, illustrated in FIG. 1 and 2, an integrated circuit die 10 is placed into a protective package 12 and bond pads 9 of said integrated circuit die 10 are connected to pins 11 of said protective package 12 via tiny bond wires 13. These pins 11 are in turn connected to tracks 14 of a printed circuit board 15.

In the more recent flip-chip technique, illustrated in FIG. 3, the integrated circuit die 10 is directly connected to the printed circuit board 15 via solder balls 16 (or solder bumps). In this technique, solder balls 16 are placed onto solder pads 17 of the integrated circuit die 10. Then, the integrated circuit die 10 is flipped and placed onto the printed circuit board 15, the solder balls establishing electrical connections between the solder pads 17 and the tracks 14. As can be seen in FIG. 4, such an integrated circuit die 10 comprises an extra metal layer, called redistribution layer (RDL). The redistribution layer comprises redistribution wires 18 connecting the solder pads 17 to the input/output bond pads 14 of the integrated circuit die 10. As it is classically practiced, a bond pad 20 is dedicated to the digital ground (VSS), and another bond pad 37 is dedicated to test the die 10. Such a test is usually performed by connecting a test circuitry to the dedicated test bond pad 37 of the die 10.

There is a need to prevent a testing of the die after a flip-chip packaging operation while saving a solder ball.

SUMMARY OF THE INVENTION

It is an object of the invention to meet the aforementioned need. Therefore, the invention relates to an electronic system comprising an integrated circuit die, as defined in claim 1.

The integrated circuit die according to the invention behaves differently either there is a solder ball on the split solder pad or not. Such a die may be used for applications in which an integrated circuit die is needed to behave differently before and after an operation of flip-chip packaging. Thus, the split solder pad of the integrated circuit die according to the invention may be used to prevent a testing of the die after a flip-chip packaging operation while saving a solder ball.

As previously mentioned, such a test is usually performed by connecting a test circuitry to a dedicated test bond pad of the die. By using the split solder pad, the test bond pad may be grounded after packaging. This is done by connecting the test bond pad to a first portion of the solder pad and connecting the VSS bond pad to a second portion of the solder pad (c.f. FIG. 5). As long as no solder ball is placed onto the solder pad, the test in enabled. However, when a solder ball connects the first and the second portions, the test bond pad and the VSS bond pads are merged, and the chip can no longer be tested.

In an embodiment, the solder pad is made of two demi-disks.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will appear more clearly upon reading the following detailed description, made with reference to the annexed drawings given by way of non-limiting examples:

FIG. 1 schematically illustrates a top view of a classical wire-bond package

FIG. 2 schematically illustrates a side view of the package of FIG. 1

FIG. 3 schematically illustrates a side view of a classical flip-chip package

FIG. 4 schematically illustrates an integrated circuit die according to the state of the art

FIG. 5 schematically illustrates an integrated circuit die according to a non-limited embodiment of the invention

FIG. 6 schematically illustrates the integrated circuit die of FIG. 5 used to prevent said die from being tested after a flip-chip packaging.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 5 shows an integrated circuit die 10′ similar to the integrated circuit die 10 of FIG. 4, with the difference that it comprises a solder pad 19′ that is split in half. More precisely, the solder pad 19′ comprises a first portion 33 and a second portion 34 facing each other, each having a shape of a demi-disk. The first portion 33 is connected to the VSS bond pad 20 via the redistribution wire 22, and the second portion 34 is connected to the test bond pad 37 via the redistribution wire 39.

When no solder ball is placed onto the solder pad 19′, the first portion 33 and the second portion 34 are not in electrical contact with each other. However, when a solder ball is placed onto the solder pad 19′, the first portion 33 and the second portion 34 become in electrical contact with each other. Naturally, the portions 33, 34 may have another shape or be laid out differently on the die 10′, as long as a single solder ball can establish an electrical contact between them.

The key feature of the invention is that the electrical connections between the bond pads linked to the different portions are different depending on whether a solder ball is placed on the solder pad 19′ or not. As a consequence, the split solder pad 19′ may be used in order to prevent the integrated circuit die 10′ from being tested after a flip-chip packaging, as illustrated on FIG. 6. In this example, the VSS bond pad 20 is chip-grounded.

As long as no solder ball is placed onto the solder pad 19′, the die may be tested via the test circuitry 36. In order to do this, one terminal of a resistance 38 is generally connected to the test bond pad 37, and a potential VSS with a high state (“1”) is applied to the other terminal of the resistance 38. As a consequence, the test circuitry 36 is automatically enabled, and the die can be tested. However, after a solder ball 35 is placed onto the solder pad 19′ in order to ground the VSS bond pad 20 via a printed circuit track 24, the test bond pad 37 becomes electrically connected to the VSS bond pad 20, and the test circuitry becomes disabled. This situation is wanted when the integrated circuit die is used in applications (that is to say after packaging), so as to avoid the die to enter a test mode. 

What is claimed is:
 1. An electronic system comprising: an integrated circuit die having: at least 2 bond pads a redistribution layer, said redistribution layer having: at least a solder pad comprising 2 portions arranged to enable an electrical connection between each other by a same solder ball placed on said solder pad, but electrically isolated of each other in the absence of a solder ball on the solder pad at least 2 redistribution wires, each one connecting one of the 2 portions to one of the 2 bond pads, a second bond pad connected via a second redistribution wire to a second portion of the solder pad being dedicated to testing said integrated circuit die a grounded printed circuit board track, a solder ball being placed between the solder pad and the printed circuit board track.
 2. The electronic system according to the previous claim, wherein the portions have a shape of a demi-disk. 